<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>实现四分之一圆</title>
    <style>
        div {
            width: 200px;
            height: 200px;
            background: maroon;
            border: 1px solid #999;
        }

        div:first-child {
            /* 实现四分之一圆的核心代码  右半圆  上右的弧度为width的100%*/
            border-top-right-radius: 200px;
        }

        div:last-child {
            /* 实现圆的核心代码  每一边为width 的50% */
            border-top-left-radius: 100px;
            border-top-right-radius: 100px;
            border-bottom-left-radius: 100px;
            border-bottom-right-radius: 100px;
        }
    </style>
</head>

<body>

    <div>四分之一圆</div>
    <div></div>
    <div>四分之一圆</div>
</body>

</html>